Identification of a primary fuel filter showing the filter restriction tap point to connect to a Hg (mercury) manometer, and the filter primer plug location. On a secondary filter,”the restriction tap point is used to measure fuel pressure on the outlet side of the filter, while the primer plug location can also be used to measure the fuel pump inlet pressure to the secondary filter.

Schematic of the basic fuel system for a series 60 four-stroke-cycle EUI engine model. (b) Close up of the series 50/60 fuel gallery inlet and outlet fittings located at the rear of the engine cylinder head Note the 0.080 in. restricted
fitting at the outlet line.

The Robert Bosch VE distributor/rotary injection pump is available with one of two mechanical governors to control the speed and response of the engine. These two types of governors and their functions are:

1. Variable-speed governor: controls all engine speed ranges from idle up to maximum rated rpm. With this governor, when the throttle lever is placed at any position, the governor will maintain this speed within the droop characteristics of the governor. The variable-speed governor and its operation are illustrated in Figures 19-77a and 19-77b with its actual location in relation to the other injection pump components being clearly shown in Figure 19-68.

2. Limiting-speed governor: sometimes known as an idle and maximum speed governor since it is designed to control only the low- and high-idle speeds (maximum rpm) of the engine. When the throttle lever is placed into any position between idle and maximum, there is no governor control.Any change to the engine speed must be determined by the driver/operator moving the throttle pedal. This governor is shown in Figure 19-77c.

The variable-speed governor can be used on any application where all-range speed control is desired such as on a stationary engine or on a vehicle that drives an auxiliary power takeoff (PTO).

All model VE pumps use a percentage of the fuel delivered to the injection pump housing to cool and lubricate the internal pump components. Since the diesel fuel will pick up some heat through this action, a bleed off or fuel return from the injection pump housing is achieved through the use of a hollow bolt with an orifice drilled into it as shown in Figure 19-74.

This bolt is readily identifiable by the word OUT stamped on the hex head, and if substituted with an ordinary bolt, no fuel will be able to return to the fuel tank from the injection pump.

Contained within the hydraulic head (outlets) of the injection pump where the high-pressure fuel lines are connected to the injection pump are delivery valves (one per cylinder) (Figure 19-73), which are designed to
open at a fixed pressure and deliver fuel to the injectors in firing-order sequence.

These valves function to ensure that there will always be a predetermined fuel pressure in the fuel lines leading to the fuel injectors. Another major function of these individual delivery valves is to ensure that at the end of the injection period for that cylinder there is no possibility of secondary injection and also that any pressure waves during the injection period will not be transferred back into the injection pump.

If secondary injection were to occur, the engine would tend to misfire and run rough. The delivery valves ensure a crisp cutoff to the end of injection when the fuel pressure drops off in the line and also maintains fuel in the injection line so that there is no possibility of air being trapped inside the line.

Within the various chapters of this book are featured a number of high-technology diesel fuel injection control systems, with DDC’s DDEC system (late 1985), Caterpillar’s PEECsystem (early 1987),and Cummins ECI system (1989)being mass-produced designs that have gained prominence since late 1985.The Robert Bosch Corporation offers electronic sensing and control of both its heavy-duty inline multiple-plunger pumps and its smaller model VE distributor pump assemblies used in automotive applications. As with the DDC and Cat systems, the high pressures necessary for injection purposes are still created mechanically by a reciprocating plunger within a barrel; however, control of the fuel rack position, and therefore of the quantity of fuel injected for a given throttle position and load, is determined by an ECU(electronic control unit) which has been programmed to output specific control signals to the governor / rack in relation to the accelerator position, turbocharger boost pressure, mass airflow rate, engine oil pressure, and temperature and coolant level.